Don't you just hate it when that drop-dead gorgeous 65/66 Mustang of yours won't start? Or when you turn on the radio and the turn signals start flashing? If you have any questions that you think I might be able to help you with, or, if I have posted something that still doesn't seem to be as clear as it could be, please feel free to ask.

Hello

There is a very large class of people that own 65/66 Mustangs that, as far as I can tell, anyway, have been, for the most part, ignored entirely. They don't really want that 100 pt. show car that is so nice and was soooo expensive that they're afraid to drive it, they also don't want to make their car capable of achieving warp factor three. They just want this car that they dearly love to be able to cruise around smoothly and reliably, without having it dump them out on the side of the road or have it start making weird noises or belching out big clouds of funky-smelling smoke. And I think, truth be told, that this is by far the largest class of Mustang owners. They take their car to some technician when what they actually need is a mechanic, and this, frequently, does not work out very well at all for the owner. They don't want to re-engineer the entire car, they just want someone to fix what broke. These are the people that I am trying help out with this blog. Some problems require a little bit of back and forth, as in, "Try this." "I tried that and it didn't change anything."" Oh. well, you probably need to try that." " I tried that and it helped, but it still isn't quite right." "Now you need to try this...." If you go to http://www.allfordmustangs.com/ and then go to the classics forums, you will be able to do that with a pretty hefty gathering of some very knowledgeable people that also happen to be very friendly. None of that ridiculous one-upmanship, no flaming or abuse, none of that stuff. Just good, solid advice from people that know what they are talking about.

Monday, March 31, 2008

Mustang gauges 1965 and 1966

This is the wiring diagram for the gauges on a 66 or a 65 that has either the GT (Performance/ Image Option) package or the Interior Decor Group, a.k.a. Pony Interior. If you click on the diagram, you will be able to see all of it, instead of just the left side. What I'm dealing with here will just be the water temp, fuel and oil pressure gauges. The ammeter gauge is a free-standing, independent system that has absolutely nothing to do with the other three gauges. The gauges on your car make up a system that supplies you with some very useful information when it is working correctly, and is a very simple system to understand and repair. What you have is a black wire with a green stripe on it coming from the back of the ignition switch going to the instrument cluster voltage regulator. The ICVR takes the 12V from the switch and, by means of thermally actuated contact points, knocks the voltage down to about 6 volts. The reason that Ford did it like this was because they had all of these perfectly good gauges of a proven level of reliability that were originally intended for a car with a 6V electrical system, and, rather than redesign and manufacture all new stuff, they just used a voltage regulator in the system. Ok, now that we have gotten that out of the way, you still have that black wire with the green stripe going from the ignition switch to the ICVR. On the other end of the ICVR you have a wire, still black/green that splits off to the three gauges. That wire plugs onto the what is the driver's side of the gauges when they are mounted in the dash. This wire brings power to the gauges. On the fuel gauge there will be a yellow wire with a white stripe that goes to the fuel sending unit in the gas tank. On the water temp gauge there will be a red wire with a white stripe that goes to the water temp sending unit, located towards the front of the intake manifold on a V8 and towards the rear of the cylinder head on a 6cyl. There will be a white wire with a red stripe going to the oil pressure sending unit, down near the oil filter. The wires going to the sending units work as a ground, with the sending unit itself determining how 'good' of a ground the gauge is getting.

If all three gauges are acting stupid on you, the problem is either the ICVR or the wire bringing the power to it. There is a dash to chassis ground wire that is hooked to the mounting screw of the ICVR, but that is what makes your dash lights and stuff go goofy on you. It doesn't have anything to do with the gauges.

If one or two of the gauges seem to be functioning normally and only one or two of them is having trouble, then the problem is almost always either the sending unit, the wire going to the sending unit, or the wire going from the ICVR to the gauge. Once in a blue moon it will actually be the gauge itself, but that happens so seldom that it really isn't even worth mentioning.

If the gas gauge is the one acting goofy the first thing that you want to do is to unplug the wire from the sending unit and, with the key in the 'On' position, ground that wire out to a suitable place on the car that isn't insulated from the rest of the car. The leaf spring shackles, for example, are in a handy location, but are completely insulated by the bushings. If the gauge pegs to full, the problem is inside the tank. The problem inside the tank is, far more often than not, the float isn't floating anymore. The brass floats cost like 5 bucks, whereas, a Ford sending unit costs nearly two hundred, and the repops cost about fifty and normally don't work. If the gauge does not peg to full, then the problem is either the wire going to the sending unit or the wire coming from the ICVR to the gauge.

If the water temp gauge is the one acting funny, again, ground the wire out somewhere and see if the gauge pegs. If yes, replace the sending unit. They also are cheap. If no, it's probably the wire going to the sending unit. People have the annoying tendency to cut that wire and then strip back both ends and tie the two ends back together. Don't do that. A brand new engine gauge feed only costs about twenty bucks, and you'll have brand new stuff that will work reliably for many years to come. If money's a bit tight, use some proper connectors of the male/female plug-in variety and wrap that to insulate it. All of what I just said about the water temp gauge is also true about the oil pressure gauge.

Thank you Bill. That is very kind of you. I've never actually used a solid state instrument cluster voltage regulator, so what I would have to say about them wouldn't mean much, but, I would assume that they were of a similar level of reliability to the solid state alternator regulators, which is, from my experience, quite good. I would also imagine that, if there are different manufacturers, some would be better than others, but, as far as particulars of the different manufacturers go, I really couldn't say. I know that Borg/Warner has always put a quality product on the shelves of auto parts stores, so, if they make a solid state instrument cluster voltage regulator, it's probably the best one out there.

That 'sending unit' title always did strike me as being backwards, also. I guess it comes from the way that the old positive ground systems worked, or possibly because, ultimately, it is responsible for sending you some useful information. But, it always did strike me as more of a receiver than a sender.

I have a weird problem with my gauges I hope you can help with. My gauges seem to read too high. Gas gauge needle is way past the 'F' when the tank is full. Also the temp gauge is pointing more towards the 'H' than it should be (alomost all the way) even thought the water temp is within range. I can live with the gas gauge, but I'd like a reliable temp gauge so I know if its really running hot.

Hi David. It sounds like it might be time to check the instrument cluster voltage regulator. It should be allowing about 6V with the key on at the wire that splits off to the gauges. If the contacts are starting to get a little sticky in there, it would make the average voltage be a little higher than it should be, and, consequently, the gauges would read a little high. It could also be that the alternator regulator is going bad on you. If it's allowing the full output of the alternator into the system, that could also have the gauges read high. I would check the instrument cluster regulator first, though.

Any thoughts on a gauge cluster (1966) that seems to be operating as the car is idling in the garage/driveway but after driving a while they all just go dead? I changed the VR thinking that may be the issue but obviously not.

Is the car still doing exactly the same thing now that you've changed the voltage regulator, or is it still messed up, but acting a little bit different? If it's still the same, I would trace that black wire with the green stripe from the back of the ignition switch that supplies power to the voltage regulator to see if it was bouncing around and shorting itself out on something while your going down the road. You could simulate that by pulling the gauge cluster out enough to get your hand on the back of the ignition switch, but leave every thing hooked up, and wiggle the back of the ignition switch around some, then wiggle the wire itself around, and see if you can duplicate that failure sitting in your driveway. Also check and see if the turn signals no longer work when the gauges die.If no, it's probably a problem with the ignition switch itself.

If the gauges still act goofy, but in a different way than before you swapped out the voltage regulator, it could be that you have a defective voltage regulator.

I just purchased a 66 Mustang and found your column. It's excellent. I am having a similar problem. Occasionally my gauges all die along with the turn signals. The problem is intermittent. I put on new ICVR in and still have the same problem.

Thanks. I try to help out as much as I can.If they work sometimes, then don't work, and they are all three working and failing at the same time, the problem would have to be the power source to the instrument cluster voltage regulator, since that and the regulator itself are all that they have in common. The problem could be the black/green wire, or the connector that attaches it to the regulator could have a bunch of corrosion, it could possibly be the connector on the back of the ignition switch, but, it will almost certainly be something pertaining to that wire.

You blog is great! This post just solved my problem... your recommendation of looking at the black/green wire from the back of the ignition was spot on. My gauges kept on going out intermittently, and it turned out that the little nut that tightens down that wire had just come loose. So happy that is fixed. Thanks!

Is it correct that the ICVR does not ground through its body? I have added aftermarket gauges and used a plastic pod. Will this be a problem mounting the ICVR to the pod? The ICVR was originally mounted to the back of the original gauges, but was that for grounding purposes?

The question of grounding the ICVR is actually a bit more complicated than just a simple yes/no. For the original design ICVRs to cycle properly, they have to have a ground, and all of the drawings show that they do indeed seem to ground themselves on the back of the instrument cluster, which has a ground wire going to bracing behind the dash. And, I've had engineers that were also very smart people explain this to me in intricate detail. They were also unsure of whether or not this ground was actually needed, because the wires going to the sending units are also a ground. With the key on the ICVR has a ground if there is any gas in the tank. With the motor running, it also has a ground if you have any oil pressure. If the motor is off, the temperature of the motor is dead cold,and the car is out of gas, but the key is on, the question could be asked about whether or not the ICVR is cycling correctly, but, in that state, it really doesn't matter and there isn't any good way of answering the question because any conceivable way of checking would involve a ground of some sort in whatever you are checking with. So, the answer would be maybe yes, maybe no, and nobody can really make a definitive statement saying either one for certain. If somebody does make a definitive statement of certainty one way or the other, they probably don't know what they are talking about.

Sorry to bore you with all of that, but, there's a little more to it than just yes or no. As far as your reason for needing to know goes, most aftermarket gauges that I've seen work on 12V, not 6V, and draw power straight from some keyed source, have a connection of some sort, either a wire or a conduit of some sort, with the appropriate sending unit, and have a provision of some sort for a ground that allows the gauge back-light to work. The ICVR isn't even used. I would say look at the manufacturer's instructions that came with the gauges and they will tell you if they need some sort of independent ground for the gauge itself, but, I don't recall ever having seen one that did. Hope that helps.

Veronica,I've been troubleshooting my gauges and this is my current problem:The fuel and temp read low, and the oil pres reads slightly below normal. I traced and tested all the sender wires and they have proper continuity and voltage from the cluster. The fuel tank is new and is grounded well, the engine is grounded well to. All of my sending units have been replaced within the last 2 years and I tested them all for proper resistance, all check good. I grounded all of the sender wires and the gauges will read full as they're supposed to, I did this with each gauge individually and all at once. Except for the fuel gauge which goes to about half then clicks and drops slowly back to around 'E'. The top of the needle appears to be burned and I think it is the only gauge that may need to be replaced. The ICVR was also replaced within a few years. I have 5-6V coming to and leaving every gauge and all have no resistance, checked with my volt meter. All grounds appear to be good, no loose connections, and every other electrical system works as advertised on the car. My gauges are my only issue. I'm stumped. I've scoured the internet and your blog and trouble-tested every method I can think of. The alt VR has been replaced with an electronic unit as well. I installed mechanical oil pressure and temp gauges (factory gauges and senders are still installed and hooked up) to monitor those systems and everything is working correctly. Any suggestions???

I just replaced the 65 gauges with idiot lights with a gauge cluster from a 66. When I turn on the headlights the blinker light bulbs come on and the temp gauge pegs at hot. I'm not sure yet if the fuel gauge is effected because the tank is full. Is this related to the dash voltage regulator? Thanks!

The symptoms that you are describing are frequently the result of not having the ground wire that goes from the instrument cluster to the dash brace connected. There is supposed to be a wire that is attached to the instrument cluster by the same screw that holds the voltage regulator onto the back of the instrument cluster, and it goes to the brace of the metal part of the dash, over to the left of where the speedo would be.

Great post! I have a 65 gt and none of the gauges work so I suspect it is the ICVR (they all show zero). Except the amp meter - it sort of moves and stays near the center. I can get a multimeter to the feed wire on the back of the ICVR and see 12V with the key on. On the wires that lead to the gauges from the ICVR, I don't see power. How does the ICVR attach to the dash? I can't quite see up there to figure out how it mounts.

On your car the amp gauge works independent of the other three gauges. On the 65 model Mustangs that came with either pony interior or the GT package, the amp gauge doesn't have the two prongs sticking out with wires connected to them. What you have is a metal loop with the main power wire passing through that loop. The instrument cluster voltage regulator has nothing to do with the amp gauge. Your problem will be either a dead ICVR or an interruption of some sort in black/green wire that goes from the back of the ignition switch to the ICVR.

Veronica - on my '65, the gas gauge and the reverse lights aren't working. Can these be related? I was reading somewhere that there is a correlation, but the person did not elaborate. Any help would be greatly appreciated.

That is going to be two different problems. The gas gauge has absolutely nothing to do with the back-up lights. If the water temp gauge seems to be working normally, then I would turn the key on and then unplug the wire from the sending unit at the gas tank, and ground that wire out on the car somewhere that it can make good contact. If the gauge pegs, the problem is inside the gas tank.

If you look at the March of 2009 section here, you will see a post titled Mustang back-up lights. That you should help with the back up lights.

HI VeronicaFirst of all, i'd just like to say what a great blog this is.I have 2 66 coupes and the wiring has been a mess on both.I've just sorted a lot of issues on one but i'm still getting a problem with the dash lights, when i pull the headlight switch on both the ind lights illuminate, along with the lights and the turn signals are a little erratic. However, when the lights are off, the turn signals dont work at all. Could it be the dash ground causing an issue ?

Assuming that the outside front turn signals work like they are supposed to, the ground from the instrument cluster to the dash could be part of the problem. It sounds like there might also be some other issues, though.I would start by pulling the instrument cluster out, cleaning everything up as far as connections, corrosion in or around the bulb sockets, and see if that accomplished anything.

I've got all the dash out now, thanks to your blog, my service manual and stuff i've gleaned off the net, i've fixed the heater, wipers, washers, dash lights, fuel, temp and oil gauges and some of the lights. The turn signals worked before i started repairing everything, so i would assume it's something i've done wrong.Could the wrong bulbs cause an issue ? when i put my meter on the battery cables i'm getting a parasitic draw of 11 voltsMike

When you say that the turn signals don't work now, do mean that, when you hit the turn signal, nothing happens, some work and some don't, or the appropriate lights come on but don't flash? That draw could be something else entirely, since the key has to be on for the turn signals to work. I did a post here in November of 09 on finding a draw which should help you out with that.

I will check the lights tomorrow but i seem to recall the turn signals dont work when the light swicth is pulled on but work when it's switched off. I've done your battery draw and i'm getting 11 volts. The engine is a later 5.0 with the motorcraft alternator F4ZU 10316, the reg and the solenoid look to be original but the coil looks more modern. Please bear in mind, the motor was all fitted before i bought it.

I've checked the lights today and the turn signals do work with lights on or off and the brake lights work ok but when the turn signals are flashing very quickly. Whilst i was testing them i temporarily lost the brake lights altogether. When i first got the car, the drivers side rear was not working correctly, i sprayed a bit of wd 40 in the holser and it was ok but the housing is very rusty and inside the bulb holder is rusty and the centre popped out tonight, the pass side is all new. Do the lights earth through the housing or the bulb holders ?

How the circuit of the lights goes is power comes in through the appropriate wires, goes through the bulbs, grounds through the socket, which grounds through the tail light housing, which grounds through the body of the car. If one of the sockets is all rusty and corroded, that could certainly cause all sorts of weirdness to occur in the lighting.

That alternator should be internally regulated. With the later motor and that alternator, your car shouldn't even have an external voltage regulator. If that regulator is actually wired into the system, that account for the draw. Also, on a later model car, the turn signals will flash faster if a bulb is burned out anywhere in the external lighting, but, your car isn't supposed to do that. With the motor running at 2000 RPMs or higher, the alternator charging like it's supposed to, the turn signals should be flashing at the same rate no matter what the condition of the bulbs, sockets, or tail light housings. I think that I would put finding and eliminating that draw at the top of my list. Once you get that sorted out, that might solve some of the other problems by accident.

First thing i'm going to do is replace the rear light housing and then run grounds from both housings to the body. The next bit is trickier because i have a wiring diagram for the 66 car but i'm not sure how the alternator should be wired in this car. I have repaired a lot of the wiring behind the dash, the engine bay and the trunk, just need to get my head round this.

I checked and that alternator does indeed have an external voltage regulator. I have discovered that there is a Taurus club, and that's the alternator/regulator set-up used in, among other things, the Ford Taurus. How many wires are going to the regulator that is on your car? And, how many wires are attached to the alternator?

When i disconnect the plug from the alternator the draw drops from 11v to 3. The regulator has 2 wires from it. A white One on the bottom terminal and a red with green stripe above it. after stripping back the tape at the front, both are cut off. According to the wiring diagram, the white should be at the top and goes to field on the alternator. The next down is a green with red stripe that goes to the fusebox, theres what looks like a grn/r wire that runs down the drivers side along with the sender wires that was hanging loose that is cut off. Theres a thick yellow which appears to be cut that i think goes on the third one down and goes to the + side of the solenoid but the diagram shows it splitting into two wires ? The bottom blade doesn't show anything clearly. The alternator has a 3 pin plug with A which is yellow and is connected to the hot side S which is blk/w and i think goes to the stator and I which goes to the firewall connector. Then there's a thick red from the hot side of alt to pos on the solenoid. Do i need the correct reg for this alternator ? or will the old one suffice ? Sorry i know it's kinda long and i hope you can understand what i've written but after peeling some of the tape back there's wires cur everywhere.

Wow. (insert smiley face here.) What you have going on is a mis-matched set of components that has also been hacked up pretty badly. The stator post on the alternator, is used for cars that have idiot lights. All 66 Mustangs came with a gauges, not idiot lights. That green/red wire that goes down the driver's side through the firewall is also for the idiot light that your car doesn't have. With all the wires that have been cut, taped, and re-directed in your car, it looks to me like the cheapest, easiest way for you to proceed would be to yank all of that junk out of there and get a new headlight harness, alternator harness and alternator for a 66 Mustang. I realize that it's awfully easy for me to sit here and spend your money, but, your alternative is to start, one wire at a time, and make those harnesses yourself. There could also be wiring that goes underneath the radiator core support, which is where the wires go from the alternator to the regulator, that are shorting out inside that lower frame piece, which would explain why you still have a draw when you disconnected the regulator plug. The headlight harness costs about a hundred dollars, and the alternator harness is about 25. That's in the U.S., though. I get the impression that you are either in the U.K. or Australia. If that is the case, I don't know how much stuff costs there, but, if they aren't straight up crazy on the money thing, the cheapest, easiest way would still be to snatch all of that junk out of there and replace it.

I dont really want to replace the alternator because of cost. The wire that goes down the drivers side is from the centre firewall connector and it looks red and off white or grey, so that is original I've repaired the thick yellow which goes from the reg to the battery side of the solenoid, and the red/blk reg ground wire, the white wants extending, the reg looks quite crusty underneath, so i might buy the one to match the alternator. Is this a 2G alternator ?

Right i've got a plan, i find a thread on vintage mustangs telling me exactly how to do this, i'll order the parts tomorrow and it's a few hours work at most, so it will probably take me all day. LolHere's the link for anyone else, that might want to do this.

I understand Veronica and your site's been invaluable on other wiring i've done on these old Mustangs.It just happens this car came with a later engine and the 3G alternator fitted and i'd just like to get it all working correctly. It still runs a performer int and holley carb.

Just an update on my turn signals lighting up on the dash when i pull the light switch. It turns out it was me, i changed some of the wires round behind the dash that were wrong but as i scribbled my diagram from the service manual, i ended up fitting two of the blue/red wires in the upper sockets instead of the lower ones. I think i got it wrong because the dash is shown upside down in the service manual. I decided to check the book again and it dawned on me what i'd done wrong, what a dork. Lol I've upgraded to a 6g power wire to the solenoid with a 200a fuse, just waiting for the new reg for the 1g to 3g conversion. The only thing i wont be able to use is the shunt style ammeter.

I wouldn't be too concerned about the 66 ammeter gauge. Many of them didn't work when they were brand new, and it is uncommon to see one that works now. The 65 ammeter gauges were a lot better. I wouldn't beat myself up too much over hooking the wires into the turn signal switch incorrectly. That is extremely easy to do, especially when referencing the service manual. That's why I posted a picture of how those wires are supposed to go. That sees much simpler to me. I'm just happy to hear that you have everything sorted out. For now, at least. (insert smiley face. )

Yeah, i read about the shunt style gauges, if need be i'll wire them to a volt gauge. I didn't get the switch wires wrong it was bulbs in the cluster, that were wrong way round.In england we have to have amber turn signals, so i'll disconnect the out on the brake light switch, then run a wire straight from the brake switch to separate the turn signals and brake lights, then i'll wire the turn signals into the reversing lights and fit orange bulbs. Thanks for your help Veronica, best mustang info i've seen and all explained in laymens terms.

Sounds like a plan to me. Those amber bulbs are getting to be kind of hard to find over here, but, we don't have the requirement for them. As long as something is blinking, you're ok. And, you are quiye welcome. I've never been a big fan of technical jargon, and, I'm guessing that I'm not the only one like that.

On the centre plug with 6 male and two female terminals that connects to the firewall plug there is a red and blue wire that runs down the pass side to next to the solenoid. Could you tell me hat that is for, it was connected wrongly to the alternator but i'm not sure where it goes.

Could you tell me where the other wires go on that connector because i cant find a wiring diagram that shows every wire on that connector and i have at least a couple that aren't connected. Also the yellow connector under the dash that has 3 bullet connections and has a blk and red wire input , i think from the fuse box.

Hi Veronica, I'm a long time stalker and your advice has helped me along quite a bit as I rebuild a 66 A code FB from the ground up. So as far as this gauge issue goes, fuel, temp, & oil aren't working. I replaced the CVR (IVR) with a new scott drake B9MZ-1084-EADJ. With the key on the J1 terminal has 11.89v, J2 (top & bottom) 11.89, and J3 is (only) .31. The black and green wire reads . 30 at fuel gauge, .29 at oil, and .30 at temp. The harness is a brand new Painless system. What am I missing?

I would unplug the blck/green wire that is bringing power from the ignition switch to the regulator and see what the reading on that was for starters. If it is something near 12V, which it probably is, since it's just a single wire transporting current for like ten inches,then your problem is that you have bought a junk voltage regulator. In this post from august of 2013 I talk about this some. http://thecareandfeedingofponies.blogspot.com/2013/08/instrument-cluster-voltage-regulator.html

In that post is a link to a person that makes extremely reliable instrument cluster voltage regulators.

Hi Veronica I have a 65 mustang and I'm having an issue with the fuel gauge, I've replaced the sending unit, gauge, ICVR. Now what I've noticed is I ran a ground from the battery to the rear of the car, put leads to the sending unit ( out of the tank) hooked up the yellow wire to the sending unit and the gauge worked great. So I proceeded to install the sending unit into the tank and hooked up the yellow wire to it and now the gauge doesn't work again. Now I've seen you say several times about a ground wire from the screw that holds the ICVR down to the gauges, but mine didn't have one. Now I suppose I could put one there, do you think it's a grounding issue with the tank? Now I've installed all mechinecal gauges ( oil, water, ammeter) and these other electrical gauges oil, water amp gauges are disconnected. Is this my ground issue? Hoping you can help, thanks much, Dennis

Hi Veronica I have a 65 mustang and I'm having an issue with the fuel gauge, I've replaced the sending unit, gauge, ICVR. Now what I've noticed is I ran a ground from the battery to the rear of the car, put leads to the sending unit ( out of the tank) hooked up the yellow wire to the sending unit and the gauge worked great. So I proceeded to install the sending unit into the tank and hooked up the yellow wire to it and now the gauge doesn't work again. Now I've seen you say several times about a ground wire from the screw that holds the ICVR down to the gauges, but mine didn't have one. Now I suppose I could put one there, do you think it's a grounding issue with the tank? Now I've installed all mechinecal gauges ( oil, water, ammeter) and these other electrical gauges oil, water amp gauges are disconnected. Is this my ground issue? Also in all the wiring manuals I've never seen a ground on the back of the gauge cluster. Hoping you can help, thanks much, Dennis Ps sorry if I posted this twice

Hi, Dennis. That could be the problem. It could also be that the tank isn't grounding out on the body as well as it could be. That can happen when there is a layer of sealer between the tank and the lip that the tank is sitting on, along with that lip being painted, and some sealer is on the screws that hold the tank. I would start by just taking a wire with alligator clips on each end, clip one to the fuel outlet of the sending unit and the other end to a good ground to see if that was the problem. If not, I would run a ground wire from the instrument cluster voltage regulator to the dash bracing behind the dash.

Hi Veronica just an update, when I wrote this post I had the car all buttoned up and I started to add fuel to the tank with no response. I had entered about 3 1/2 gal with no response, that's when I wrote to you. The next day after talking to you, I didn't Change anything but when I got to about 4 gallons I started to notice the gauge starting to move. So I kept adding until I got to around 12-13 gallons and it just kept climbing. Because of the blogs I've read about how if you get repops of sending units and that about 1 in 5 actually work my concern was that I had got one too that didn't work. Thank you for your insights and information, and I have enjoyed reading and listening to what you have to say. God bless you and keep up the good work. I'd send you a pic of the car but I couldn't find a way to do it. Anyway thanks again, your friend Dennis.

Hi Veronica,Stalker here for a couple of years and just let me tell you that your little blue butterfly has become synonymous in my head with "excellently explained advice" and also has a calming influence on my mood when I have had a bad Mustang day. So, Thank You.In your reply to Dennis's post you said that he might run a ground wire from the ICVR to the brace behind the instrument cluster. He has a 65 and he said that there was no ground wire. I have a 65 and there is no ground wire either. I was under the impression that the 65 ICVR did not have a ground running directly to the brace behind it.I have had many electrical/gauge issues with this car and I thought that it may be a ground issue so I ran a ground wire to the brace behind the instrument cluster. When I did the wire coming into the ICVR got so hot within a matter of seconds that it melted the jacket off the wire and melted some of the other wires that it ran with in the harness. Did I do something wrong?

Hi Veronica,Stalker here for a couple of years and just let me tell you that your little blue butterfly has become synonymous in my head with "excellently explained advice" and also has a calming influence on my mood when I have had a bad Mustang day. So, Thank You.In your reply to Dennis's post you said that he might run a ground wire from the ICVR to the brace behind the instrument cluster. He has a 65 and he said that there was no ground wire. I have a 65 and there is no ground wire either. I was under the impression that the 65 ICVR did not have a ground running directly to the brace behind it.I have had many electrical/gauge issues with this car and I thought that it may be a ground issue so I ran a ground wire to the brace behind the instrument cluster. When I did the wire coming into the ICVR got so hot within a matter of seconds that it melted the jacket off the wire and melted some of the other wires that it ran with in the harness. Did I do something wrong?

Hi Rhett, Dennis here. If you ran a ground directly off the back of the icvr( attached by the screw holding it down) it shouldn't be a problem. But if sounds like you attached the ground to one of the blades of the icvr and that will quickly give you a direct ground and cause the wires to burn. The dash cluster is grounded to the car via the back of the dash cluster. If you dash lights are working when you turn them on then it's grounded. Take s jumper wire and connect the dash cluster and the dash screw hole then test your dash lights if they work then your grounded. Not sure what problem your having but I'm sure Veronica will be able to help. Let me know if I can help in anyway. Thanks Dennis

Dennis is correct. The ground wire is supposed to be attached to tab on the ICVR by the screw that holds the ICVR onto the back of the instrument cluster. With the ground attached like that, there isn't really any way that the wiring could be overloaded to the point of melting. If, on the other hand, the ground was attached to the output terminal of the ICVR, which is is the one with the black/green wire that splits off to the gauges, what you have described is exactly what would happen.

And thank you. That is very kind of you. I took that picture of the butterfly on one of the trips that hubby and I took to the Great Smoky Mountains National Park.

Well that is why I asked. I had it connected correctly then. I ran a ground wire from the screw that holds the ICVR to the back of the dash to the brace behind the cluster. Then hooked up the male and female wires to the ICVR. Turned the key and smoked billowed out of the dash. The ICVR was new from NPD. I bought a different one after the first one burnt that was supposed to be better but when I hooked it up, that one fried too. (This one fried slower and I didnt have that ground hooked up anymore) I saw the post of the "Nameless man who makes the really sturdy" one and I ordered one of those yesterday but I dont really dare hook it up until I find whats really causing the wire to heat up. Any ideas of where I could look? Ive pulled the harness out and replaced the wire and I am attempting to replace the fuse box as well although none of the fuses were blown.

Hi again Rhett, wow that sucks!! Here's what happened to me. I went to auto zone and bought a new turn signal flasher, put it in then about three days later the flasher shorted itself inside and caused it to burn up the turn signal loom. I caught it before it burned all my wiring but it did burn the whole turn signal loop. So in an effort to save money and fix this issue myself I ( and here's where you come in) unraveled all the electrical tape holding all the dash wiring behind the gauge cluster and went thru it one wire at a time, traced where it's suppose to go and I found several dead end wires that were not safely protected by either shrink tuning or was disconnected. I'm afraid that you might have one of these dead end wires grounding out to the frame or dash. I know it's a pain in the you know what but I think that's where you need to start. Plus your going to have to repair wires anyway. Could be something as simple as your cigarette lighter not hooked up properly, but somethings grounded. I'd also look at your ignition switch. If I can be of any help please don't hesitate to ask. Best of luck Dennis

Thanks for this great and interesting blog. I got all the needles of my gauges to move to Hot, Full and High. by grounding them proving that they did work and the wiring was complete to each gauge. Great clear cut advice on that. (I've spent a good amount of this summer replacing the under dash and under hood wiring harnesses on this once white now red 65 GT.) This Pony with pony interior had been stuck in a barn for 20 years and who knows what before that? It did have a huge mouse nest in the drivers side of the cowling which was the first order of business to remove. What a mess. You'd tear up driving from the smell! I even pulled out several tiny skeletons!Someone had made a mess of the wiring too, but by some miracle the car worked with dim lights and weird gauges when a bought it. I'm slowly getting everything working again and it's a really fun car with a powerful 4v 289 with headers, 4spd and GT handling package. Having gauges work would be really nice so I'm working on that right now. Here is my question: I replaced the sending unit and gas tank, connected everything and put 9 gallons of gas in and it's only showing 1/4 tank. Any idea why? Thanks Roos

It's amazing how much damage something as small as a mouse can do to a car.

I think that the first thing I would try would be to drain the tank, and then put 4 or 5 gallons of gas in it. If the needle barely moves as a result of that, you can pull the sending unit out and bend the arm that the float is hooked onto to make the float sit lower in the tank when it's empty. That's kind of a trial and error process, but, you can get it so that the gauge reads about right. These gauges weren't tremendously accurate all the way up and down the scale when they were brand new, but, they were pretty close at full, empty, and half a tank.

Hey Roo, Dennis here. Veronica is the expert here, I'm just throwing my 3 cents worth in as well. What Veronica has said is correct, here's a couple if things you might want to check. Take the time to drain your tank and pull the sending unit out. Sometimes the float can have a crack in it ( mine did) and will cause the float to set lower in the tank and making the reading inaccurate. I've been told that if your going replace the sending unit to hold onto your old one if its still in good shape and rebuild it, it will be 10 times better that the aftermarket ones. Here's what I did, I pulled my old one replaced it with a Scott drake model. While I had it out I ran a piece of wire from the battery to the rear of the car and used that wire as a direct ground to the battery, used a jumper wire from the yellow wire ( sending unit wire) ran both wires to the sending unit. While holding the sending unit in my hand ( in the correct configuration as it would be sitting in the tank) and I proceeded to adjust the sending unit wire arm till it read correctly on the gauge and key on. It will take a little time but well worth the effort. Once you get it dialed in you'll be happy you took the time. I actually had to cut some of the metal on mine to get the arm to go up hi enough to show full. I had to bend the arm a little too. Before I did anything with the sending unit I Tested it to make sure it was getting enough ohms running thru it to show that it would work properly. After the adjustment I put it back in and it worked great ( and changed the float). Make sure you don't pinch the gasket for the sending unit while trying to put it back together. I did that and then had to wait a week till I could get another one here. Bummer!! Anyway many thanks to Veronica for her knowledge and I hope she doesn't get mad at me for piping in on the conversation. I get the emails on the blog as well. Good luck Roo and if I can help please don't hesitate to ask. Many blessings to you and Veronica, Dennis

By all means, Dennis, and, anyone else, for that matter, please feel free to jump right in on this or any other conversation. Nobody knows everything, but, collectively, we can all work together to persuade these cars to behave themselves.

Hi Veronica, in an effort to improve the night time visibility of the instrument cluster on my 66 Mustang 6 cyl.,I removed it and replaced a couple of bad bulbs and ran a ground wire from the cluster to an existing ground screw on a metal brace. When I put it back together,the dash lites worked great but the fuel, temp and oil gauges all pegged when i turned on the ignition. I have since removed the ground wire but the gauges still pegged.all worked before I opened up the dash cluster.your thoughts would be greatly appreciated.

Hi, Beverly. Sorry about the delay. I have things set here so that I have to ok the comments before they get posted. If the comment has anything to do with an old Mustang I post it, but, some people aren't as well behaved as they ought to be. The internet can be a very strange place sometimes.

What you are describing sounds like an instrument cluster voltage regulator failure. I would start by unplugging the black wire with a green stripe from one of the gauges and check and see if showed 12V with the key on. If yes, then the contacts inside the ICVR have gotten stuck together. It's odd that it picked then to go out on you, but, stranger things have happened. If it received a quick surge of current somehow, that could cause the contacts to stick.

Hi All,I stumbled across this last week because I am having a similar issue. I have a 65 falcon and my Fuel and Temp gauges are acting very strange. Mostly pegging to the right. The regulator in mine wasn't grounded and looked O.E. I verified wiring against a diagram and installed a new, solid state regulator after reading through these comments. The issue seems to be the same and the new regulator gets very hot. I can't find any shorts or damaged wires and everything looks correct against the factory diagram. Any thoughts?

Sorry this took so long. If the gauges are pegging and the regulator is heating up, you would just about have to have a short somewhere. If there is no obviously damaged wiring it might be time to start unwrapping the harness.